In general, it is known that thin film is formed on the surface of solid material in plasma and a solid surface characteristic is improved by injecting an ion. Film formed by using of a plasma including metal ion and metalloid ion can strengthen the characteristics of abrasion resistance and corrosion resistance of a solid surface, so that it is useful as protective film, optics thin film and transparent conductivity film. As an approach to generate the metal ion and the metalloid ion, there is a vacuum arc plasma method. A vacuum arc plasma is formed by an arc discharge generated between cathode and anode, namely after a cathode material evaporates from an cathode spot existing on the cathode surface, the plasma is formed by this cathode evaporation material. In addition, when a reactivity gas and/or an inert gas (rare gas) are introduced as ambient atmosphere gas, the reactivity gas and/or the inert gas also are ionized at the same time. By performing the thin film formation and the ion injection on solid surface by means of such a plasma, surface treatment process can be carried out.
Generally, in the vacuum arc discharge, vacuum arc plasma constituent particles such as cathode material ion, electron and cathode material neutral particle (including atom and molecule) are emitted from the cathode spot, and at the same time, the cathode material fine particles referred to as droplets of size of nanometer order to several hundred micron (0.01-1000μm)are also emitted. When these droplets bond to a base member surface, the uniformity of thin film formed on the base member surface is lost, and it becomes defect product of thin film.
As a method to solve above problem of droplets, there is a magnetic filter method (non-patent document 1). As shown in FIG. 12 illustrating an outlined schematic diagram of internal structure, in this magnetic filter method, the vacuum arc plasma is transported from plasma generating section 101 to plasma processing section 103 through bellows-shaped duct 102 curved to be S-shaped. According to this method, the emitted droplets D are adhesion-captured (captured) on an inner peripheral wall of bellows-shaped duct 102. In addition, curvature magnetic field is formed by means of electromagnet 104 constructed from windings disposed along duct 102, and the plasma stream is bent by said curvature magnetic field, so that plasma P is effectively moved to the plasma processing section 103.
However, there are the following problems in said magnetic filter method. Since the droplets D accumulate on the inner wall of bellows-shaped duct 102, it is necessary to remove the droplets regularly. However, the operation is not easy, because the duct 102 is formed in the shape of bellows. Additionally, though big droplets D are captured to duct 102, small droplets D flow to the plasma processing section 103 attending with plasma P and there is a danger that they bond on the surface of article being processed 105. Besides, droplets D which did not adhere to the wall surface repeat the irregular reflection by the inner surface of bellows-shaped duct 102, so that they reach the plasma processing section 103 and the similar damage is given to the surface of article being processed 105. In addition, when droplets D accumulate on the inner wall of duct 102 to thickness of around 0.5 mm, the stack thing comes off from the inner wall and it might contaminate plasma P as an impurity. Furthermore, it is technically difficult to form steel materials to bellows-shaped duct 102, and besides, there is a defect to become expensive.
In order to solve this problem, Japanese Patent Laid-Open No. 2002-8893 (patent document 1) is published and a plasma processing device shown in the outlined schematic diagram of FIG. 13 is proposed. Additionally, in FIG. 13, reference numeral Gt is a gas introduction system, numeral Gh is a gas exhaust system, and numeral V shows a power source. In this conventional plasma arc processing method, as shown in FIG. 13, a vacuum arc discharge is done under the vacuum atmosphere in which reactivity gas was introduced if necessary, so that plasma P is generated and this plasma P is flown into the plasma processing section M. The surface treatment process by plasma P is done for the article being processed 230 disposed in this plasma processing section M.
The plasma stream emitted from the plasma generation section E is bent in the almost perpendicular direction not facing the plasma generation section E by the curvature magnetic field, and is flowed into the plasma processing section M. The droplet capturing section H by which droplets are captured is arranged at the position facing the plasma generation section E. In this plasma processing method, the plasma stream is branched in the almost perpendicular direction from the droplet stream by the curvature magnetic field, and the droplet capturing section H is perfectly separated from the plasma stream passage. Therefore, the capture and removal of droplets D are done easily, and the mixture of droplets D to the plasma processing section M can be prevented.
[Patent Document 1] Japanese Patent Laid-Open No. 2002-8893
[Non-Patent Document 1] A. Anders and R. A. MacGill, Surface and Coatings Technology 133-134 (2000) 96-100